Very interesting, yet it left me totally confused as to what the answer to my question is!

Galactic Radiation

“Galactic cosmic radiation — also called galactic cosmic rays — is the kind of radiation that researchers are most worried about. It’s made up particles, bits and pieces of atoms that were probably flung off from the aftermath of supernovas. The majority of this radiation, roughly 90%, is made up protons ripped from atoms of hydrogen. These particles travel around the galaxy at almost the speed of light.

And then they hit the Earth. This planet has a couple of defense mechanisms that protect us here on the ground from the impact of galactic cosmic radiation. First, Earth’s magnetic field both pushes away some of the particles and blocks others completely. Then, the particles that make it through that barrier start to encounter the atoms that make up our atmosphere.

If you drop a big tower made of Legos down the stairs it will break apart, losing more pieces every time it hits a new step. That’s a lot like what happens to galactic cosmic radiation in our atmosphere. The particles collide with atoms and break apart, forming new particles. Those new particles hit something else and also break apart. At each step, the particles lose energy. They get a little slower, a little weaker. By the time they “come to a stop” at the ground, they aren’t the galactic powerhouses they once were. It’s still radiation. But it’s much less dangerous radiation. Just like it would hurt a lot less to be hit with one Lego block, than with a whole tower of them.

All of the astronauts we’ve sent into space so far have, at least partially, benefited from Earth’s protective barriers, Francis Cucinotta told me. He’s the director of the NASA Space Radiobiology Program, the go-to guy for finding out how radiation hurts astronauts. He says, with the exception of Apollo flights to the Moon, the human presence in space has happened within the Earth’s magnetic field. The International Space Station, for instance, is above the atmosphere, but still well inside the first line of defense. Our astronauts aren’t exposed to the full force of galactic cosmic radiation.

They’re also exposed to it for a relatively limited amount of time. The longest spaceflight ever lasted a little over a year. And that matters, because the damage from radiation is cumulative. You simply can’t rack up as much risk on a six month jaunt to the ISS as you could, theoretically, on a multi-year excursion to Mars.

But what’s interesting, and concerning, is that even with those protections we do see signs of radiation damage to astronauts, Cucinotta told me.

The big thing is cataracts — changes in the lens of the eye that make it more opaque. With less light able to get into their eyes, people with cataracts lose some of their ability to see. In 2001,

What Happens to Body in Space?

Human beings living on Earth are effected by gravity because about two-thirds of our daily activities are standing or sitting. Great amounts of body fluids such as blood pool in the lower part of the body. The human body is equipped with various mechanisms to oppose gravity to maintain sufficient blood flow to the brain.
In microgravity environment, the quantity and the distribution of body fluid alter, being free of the gravitational effect. This is the concept of “fluid shift.”